Primary Cooling System

 

This system consists mainly of the following:

An air conditioning valve

This is located downstream of each pressure reducing and shut off valve, and is an electro magnetic valve that cuts off or admits airflow at determined rates, resulting from the gradual variation of outlet cross-section throughout the opening and closing operating time, which is :

Opening: 30 seconds

Closing in flighty and on the ground: 20 seconds

In addition, the safety function enables the valve to close in less than 2 seconds.

It is possible to test this valve by means of the COND VALVE switches IH866 located on the Flight Engineer’s panel.

Mass flow control valve

It is an electro pneumatic valve. It limits the airflow to 45 Lb. /min. in normal operation.

This airflow can be increased to 53 Lb. /min. when the air conditioning valve switch is in the BOOST position.

The airflow is automatically decreased to 19 Lb. /min. when an excessive air temperature is detected downstream of this valve (205*C).

It is possible to test this valve by means of a rotary test switch located on the Flight Engineer’s panel.

Primary heat exchanger

The function of the heat exchanger is to limit the Cold Air Unit compressor inlet temperature to 200*C approximately in normal operation. It is a compact plate and fin type exchanger, that permits a cross flow of two runs of charge air interlacing a single run of cooling air.

Ram air control valve

This valve operates to control the airflow through the primary heat exchanger in order to keep the system performances at cold temperature. The valve is pneumatically operated. It is operated by the cooling air duct thermostat when the latter detects a temperature of 25*C and by the primary heat exchanger thermostat when the latter detects a temperature of 100°C. This double operation makes it possible to have a correct temperature of the primary heat exchanger downstream airflow.

 

Secondary Cooling System

 

Cold air unit (bootstrap)

The cold air unit consists of a centrifugal compressor and an expansion turbine mounted on the same shaft. Lubrication of the ball bearings is achieved by a continuous flow of lubricating oil. The cold air unit is provided with a three position turbine nozzle corresponding to three different outlet areas.

The blades of the outlet nozzle are operated by a pneumatic actuator automatically controlled by the Cold Air Unit absolute pressure switch (threshold: 40 psi), landing gear relays and an air conditioning valve switch when it is in the BOOST position.

The cold air unit housing is sufficiently resistant to retain loose parts if the rotating assembly breaks.

Cold Air Unit Operation.

The temperature and pressure of conditioning air are increased in the compressor, the air is cooled in the secondary heat exchanger and the fuel heat exchanger; its expansion rate is high in the turbine.

Air expansion in the turbine provides the energy to drive the compressor, at the same time lowering the temperature by 100°C.

Secondary heat exchanger

The function of this heat exchanger is to lower the fuel heat exchanger inlet air temperature to 190”C approximately in normal operation.

It has the same physical characteristics as the primary heat exchanger; it is also installed on the cooling air system.

Fuel heat exchanger

This exchanger is designed to reduce the conditioning air temperature at the turbine inlet to the lowest value compatible with its volume and permissible inflow.

Made of stainless steel, it is of the compact plate and fin type and permits a cross flow of six runs of fuel and one run of conditioning air.

Intercooler water drain swirler

It is associated with the intercooler drain valve; its function is to remove condensation water from the conditioning air in order to prevent turbine erosion

Cold air unit by pass system

The temperature control valve is the main component of this system.

This valve controls the air temperature at the cold air unit outlet in accordance with the value selected on corresponding temperature control selector. It is an electro pneumatic valve controlled by two different electrical circuits (independent torque motors)

-          The automatic control circuit via the automatic temperature controller

-          The standby control circuit via the temperature controller integral with the temperature control selector. If either circuit  fails, the other one is not affected.

 

Cooling Systems

 

Air heat exchanger cooling air system

The cooling air is bled at two points:

-          At high speeds, the air is bled at the engine air inlet.

-          At low speeds (lower than 0.6 M), the air is bled on the nacelle side

These two bleed points are interchangeable due to an automatically operated flap. The airflow can be increased if air ejectors operate, they are used when the air bled on the engine inlet or nacelle is not sufficient for cooling. The ejectors are supplied by air bled downstream of the air conditioning valve through an ejector control valve. This electro pneumatic valve is controlled by a solenoid; it opens when the solenoid is electrically supplied and closes when the solenoid power supply is cut out.

The solenoid is electrically supplied when the main landing gear is down locked.

The valve has no manual control.

Cooling fuel system of fuel heat exchanger

The fuel control valve is the main component of this system. This electric valve has two operating modes, manual or automatic, this is determined according to the FUEL VALVE switch position.

In automatic mode, associated with its sensing elements (three sensors and a controller) it enables the cooling of the fuel supply to the fuel heat exchanger, when the air temperature at the heat exchanger outlet is greater than 15°C, and when temperature at the heat exchanger inlet is greater than the fuel temperature. If one of these conditions is not fulfilled the fuel control valve closes.

 

Cold Air Unit Outlet Ice Sensor Transducer and Water Separator

 

Cold Air Unit outlet ice sensor transducer

The ice sensor transducer is located downstream of the cold air unit. It transmits an electrical signal to the temperature controller according to the minimum temperature downstream of secondary cooling system, in order to prevent icing downstream of this system.

Water separator

When the aircraft altitude is lower than 30,000 feet approximately, the water separator removes 80% of the water in suspension in the conditioning air and expels it overboard.

Above 30,000 feet where the layers of atmospheric air are dry, the water separator is by-passed by means of a valve controlled by an electric actuator in order to reduce the drop in air pressure. If the by-pass system is open by means of the water separator internal by-pass electric actuator, the drain orifice is closed, which prevents conditioning air flowing overboard at high attitude.

 

Distribution System

 

The distribution chamber is located at the distribution system inlet; it collects the air supplied by the groups in order to provide air conditioning of all compartments if one group fails. The non return valves prevent the air returning to the air conditioning groups. In normal operating conditions the distribution of airflows enables air supply of the various compartments.

Downstream of the water separator, a cabin isolation valve closes automatically in the event of a duct overheat in order to prevent hot air flowing to the cabin if the engine breaks.

This electric valve is associated with a warning light, and it is possible to check its operation when it closes.

 

Warning and Safety Systems

 

Each air conditioning system has a safety system to prevent overheat, overpressure, leaks and dust ingestion.

High temperature safety

The overheat thermo-switches cause the air conditioning valve and mass flow control valve to close.

In the event of fuel heat exchanger over-temperature (95°c), the fuel control valve opens. The distribution duct overheat (210°C) causes the shut off valve, cabin isolations valve and two adjacent cross-bleed valves to close. In this case the group is no longer operative.

The pneumatic temperature sensor associated with the mass flow control valve controls the temperature downstream of the primary cooling system by limiting the airflow (19 ~b. /min.), if the temperature detected downstream of the cooling system reaches 205°C.

Overheat test and air conditioning valves

A rotary test switch which is located on the Fight Engineer’s panel, enables checking of overheat detection devices.

Cabin isolation valve closing is tested by pressing the DUCT warning light.

Overpressure safety

When the over-pressure switch operates (85 psig) the shut off valve closes. Operation of the downstream turbine overpressure switch causes the air conditioning valve and mass flow control to close. On the water separator, an internal flap opens automatically when the upstream and downstream differential pressure reaches 4 psi.

Leak detection of cold air unit double wall

The compressor housing and upstream and downstream ducts are provided with double walls in order to prevent hot air leaks in the wing compartment. When the Cold Air Unit leak detector or Cold Air Unit double wall pipe leak detector operates, the LEAK warning light comes on.

Dust

A dust centrifuge provided with a dust outlet is mounted on the system.

Fuel

The fuel heat exchangers and the partitions separating the fuel from the ambient and conditioning air are of a double wall construction. .

The wall interspace is connected to a drain system enabling detection of air or fuel leaks during maintenance checking on the ground.

Smoke detection (See the picture below)

Four high sensibility smoke detectors installed downstream of the water separators monitor the air blown from the air conditioning groups, the airflow speed being very high. On Flight Engineer’s panel, an AIR GENERATION rotary switch enables testing of associated detectors and systems:

-          Four SMOKE amber warning Lights from 1 to 4 enable location of smoke detection;

-          Four FAULT yellow caption lights from 1 to 4 which indicate failure of smoke detection systems.